1. Field of the Invention
The present invention relates to a recording method and a recording apparatus for recording information such as images, characters, etc., especially, information such as color images, characters, etc. employing respective KCMY color toners on a recording medium.
2. Description of the Related Art
To record the image, the characters, etc., there is the recording method of fixing an image receiving sheet and a transfer sheet to overlap them and exposing them by the laser. In this case, the image receiving sheet is wrapped on a drum to direct an image receiving layer upward, and the transfer sheet is wrapped on the drum to overlap a toner layer with the image receiving layer. A recording head for executing the laser exposure is reciprocally moved in parallel with a rotation axis of the drum. A laser beam is emitted from the recording head and is irradiated as a plurality of spots. As shown in FIG. 6, a spot arrangement comprised of a plurality of the spots Ls"" are aligned one-dimensionally along the moving direction of the recording head. In this recording method, the rotation direction of the drum is set as the main scanning direction, and the moving direction of the recording head is vertical to the main scanning direction so called a sub-scanning direction. Accordingly, if a rotational motion of the drum and a linear motion of the recording head are combined with each other, the spots can be scanned on the transfer sheet and thus desired images can be transferred onto the image receiving sheet.
In the above recording method, the optical energy of the laser beam is changed into the thermal energy by the photothermal conversion layer at the recording spot portion onto which the laser spot is irradiated.
The heat is generated in an instant, so that the moisture and the organic solvent contained in the photothermal conversion layer and the toner layer are volatilized to generate gas. For this reason, in the case of the above recording method in which the image receiving sheet and the transfer sheet are laminated and the action layer to react with the laser beam is put between two sheets, the generated gas is difficult to escape into the air and such gas remains between the image receiving sheet and the transfer sheet.
Concerning this condition from a microscopic point of view, the generated gas is easy to escape at both ends of the spot arrangement in the sub-scanning direction (the right side or the left side in FIG. 6). However, since the generated gas at the almost center portion of the spot arrangement is difficult to escape to said both ends, such gas still remains at the almost center portion of the spot arrangement of which characteristics can be further explained as follows.
In FIG. 6, as to the upper side of the spot arrangement, or the upstream side of the main scanning direction, the area can be regarded as a post recorded area where both a toner sheet and an image receiving sheet keep enough heat in-between so that the adhesive condition is still made, to which makes gas difficult to escape from each spot. On the other hand, the right side of the spot arrangement, or the upstream side of the sub-scanning direction, this area can be regarded as a pre-recorded area, by the main scanning being performed previously, where both temperature between a transfer sheet and an image receiving sheet is almost back to a normal with lowering the adhesive power which allows gas to escape in-between. Turning now to the left side of the spot arrangement, or the downstream side of the sub-scanning direction, this area can be regarded as an open ended space to which gas can always escape. Finally, as to the lower side of the spot arrangement, or the downstream side of the main scanning direction, since this area is not yet recorded, gas can escape.
Summarizing the above mentioned four-divided areas for the gas to escape, from both the distal end portions of the spot arrangement which is aligning along the sub-scanning direction, it is possible for gas to escape into the respective outside area, while it is difficult for the gas generated to be closer to the center spot of the spot arrangement to provide with such an escape area in the sub-scanning direction. Concerning this circumstance, most gas generated under the spot arrangement has no chance to escape to the sub-scanning direction, then it shows a tendency such as to escape to the downstream side of the main scanning direction, in other word, to the unrecorded area.
Now, turning to the main scanning speed, which is characterized of its speed being far faster than that of the sub-scanning speed, there arises a problem such that after the main scanning speed reaches the gas-escaping speed in the main scanning direction, laser irradiation is performed onto the toner sheet having the image receiving sheet underneath but gas remains in-between.
In other words, the generated gas enters into a space between the toner layer and the image receiving layer at the almost center portion of the spot arrangement where the toner layer and the image receiving layer are brought into the state that they are not tightly adhered to each other. In this state, the toner layer cannot be transferred onto the image receiving layer at the portion to which the laser beam is irradiated, so that the situation might be caused such that the portion of the final image is not colored or the color of the portion is dulled. If this situation is viewed macroscopically or visually checked, a stripe having a width of the spot arrangement (longitudinal stripe) 3 appears in the drum rotation direction, as shown in FIG. 6, and thus the image becomes defective.
For example, if the spot arrangement with 32 spots are arranged to have a distance of 10 xcexcm (2540 dpi) between neighboring spots, the width of the spot arrangement is 230 xcexcm. Also, if 256 spots are arranged to have a distance of 10 xcexcm (2540 dpi) between neighboring spots, the width of the spot arrangement is 2560 xcexcm (2.56 mm). If this width of the spot arrangement becomes wider, the gas at the center portion is more difficult to escape. If this is watched by visual check, such gas is ready to monitor as the uneven image.
Further, in the state that the gas stays in the almost center portion of the spot arrangement and thus the toner layer and the image receiving layer are not tightly adhered, the heat generated by the photothermal conversion layer of the transfer sheet is not ordinarily flown to the image receiving layer side, and thus the transfer sheet side is filled with the heat. Thus, the temperature of the photothermal conversion layer and the toner layer of the transfer sheet is increased to exceed the normal temperature. In this manner, when the temperature rises enough to decompose the photothermal conversion layer and the toner layer, the gas is generated much more, so that the photothermal conversion layer and the toner layer are melted and decomposed to cause the abnormal state. If such state is brought about, the concentration becomes lower in the center portion or the photothermal conversion layer that is not essentially to be transferred is transferred onto the image receiving layer, whereby the image becomes more seriously defective.
The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a recording method and a recording apparatus in which the gas generated in a recording spot portion never remains between a toner layer and an image receiving layer in a recorded area and to achieve prevention of the image defect depending on an spot arrangement.
In order to achieve the above object, a recording method in this invention enables a recording of a desired image on a recording medium, which is provided by laminating a toner layer of a transfer sheet as heat-mode sensitive material and an image receiving layer of an image receiving sheet, by exposing the recording medium while moving the recording medium in a main scanning direction and also moving a plurality of aligned laser beam spots in a sub-scanning direction that is perpendicular to the main scanning direction, and exposure is carried out by laser beam spots of which spotting direction is inclined such that a spot on an upstream end in the sub-scanning direction is positioned on a downstream side in the main scanning direction rather than a spot on a downstream end in the sub-scanning direction.
In this way, gas generated in the recording spot portions can escape not only toward the downstream side of the main scanning direction but also toward the downstream side in the sub-scanning direction during the periods of the gas being generated. As a result, such gas never remains between the toner layer and the image receiving layer in the recorded area so that the adhesiveness between the toner layer and the image receiving layer can be held properly, the image defect depending on the spot arrangement can be prevented, and the good image can be obtained.
According to further aspect of this invention, it comprises a recording medium fixing member for fixing a recording medium which laminates a toner layer of a transfer sheet as heat-mode sensitive material and an image receiving layer of an image receiving sheet, said recording medium fixing member being moved in a main scanning direction, and a recording head which is moved in a sub-scanning direction, that is perpendicular to the main scanning direction, while exposing a plurality of aligned laser beam spots onto the recording medium respectively in response to image information, laser beam spots are aligned to be inclined such that a spot on an upstream end in the sub-scanning direction is positioned on a downstream side in the main scanning direction rather than a spot on a downstream end in the sub-scanning direction.
According to this recording apparatus, the laser beam spots are aligned to be inclined such that the spot on the upstream end in the subs-canning direction is positioned on the downstream side in the main scanning direction rather than the spot on the downstream end in the sub-scanning direction. In such arrangement of the laser beam spots, if the rotational motion of the recording medium fixing member and the linear movement of the recording head are combined with each other, the gas generated in the recording spot portion can be fed subsequently to the downstream side of the sub-scanning direction with the movement of the recording head. That is, the gas generated in the recording spot portion can escape to the unrecorded area sequentially, and the residue of the gas between the toner layer and the image receiving layer in the recorded area can be prevented.
In the recording apparatus according to another aspect of this invention, an inclination angle of aligned spots is set to a range of 5xc2x0 to 85xc2x0 to a vertical scanning axis.
In this recording apparatus, since the inclination angle of the laser beam spots that are one-dimensionally aligned is set to the range of 5xc2x0 to 85xc2x0 to the vertical scanning axis, the action for feeding the gas generated at the recording spot portion to the downstream side of the sub-scanning direction can be obtained without fail. More particularly, if the inclination angle of the laser beam spots that are one-dimensionally aligned is set to the range of 0xc2x0 to 5xc2x0 to the vertical scanning axis, the sufficient feeding action cannot be attained because of the small inclination and thus the gas remained in the recorded area is present. Also, if the inclination angle of the laser beam spots that are one-dimensionally aligned is set to the range of 85xc2x0 to 90xc2x0, the inclination is excessively large and the high speed recording employing a plurality of desired spots cannot be achieved. In contrast, if the inclination angle is set to the range of 5xc2x0 to 85xc2x0, the good gas feeding action can be achieved and also the high speed recording can be achieved.